Adenocarcinoma of the prostate gland is the most frequently diagnosed cancer in men and remains the second leading cause of death in mature men. It is estimated that a man has a one in ten chance to develop prostate cancer. The reported incidence of prostate cancer has been increasing in the past ten years. The annual incidence of prostate cancer in the U.S. grew from 165,000 reported cases in 1993 to 318,000 reported cases in 1996. This increased incidence is believed to be primarily due to increased life expectancy, prostate specific antigen (PSA) screening, and improved diagnostic techniques, including transrectal ultrasound (TRUS). These factors have also lead to an increase in the number of younger men being diagnosed with localized prostate cancer. These trends are expected to continue.
The standard treatment regimens for prostate cancer are: (1) watchful waiting; (2) radical prostatectomy; (3) external beam radiation; and (4) prostate brachytherapy (radioactive seed implantation). Although "watchful waiting" is an appropriate choice for some men, the majority diagnosed with early stage prostate cancer will either request or require treatment of some kind. Radical prostatectomy is the "gold standard" for prostate cancer therapy, but is associated with significant morbidity, such as incontinence and impotence. While external beam radiation has proven to be an effective treatment, a long treatment time is usually required. The rising incidence of earlier stage prostate disease in younger patients with longer life expectancies has brought into focus both treatment effectiveness and the quality of life. The recent development of transperineal prostate brachytherapy as an effective treatment option has provided an alternative for patients seeking to preserve their prostate function as well as control the cancer.
Prostate brachytherapy, which can be performed as a single outpatient treatment, is recommended for patients with early stage (prostate-confined) disease. For patients with a high likelihood of disease located outside the prostate, it is often used as a "boost" following external beam radiation treatments. Because prostate brachytherapy is associated with a lower incidence of incontinence, impotence and rectal injury, it is emerging as a medically successful, cost-effective outpatient treatment in treating localized prostate cancer.
Prostate brachytherapy involves the accurate placement of radioactive materials, known as seeds, into the prostate gland according to a predetermined dosimetry plan. FIG. 1 shows a template-guided implant needle 10 inserted into the prostate gland 12 under the guidance of an ultrasound probe 14, which is inserted into the rectum of the patient. Successful execution of the brachytherapy procedure is the culmination of several specific steps. First, a prostate volume study using the transrectal ultrasound probe is performed. In the volume study, the patient lies on his back, the ultrasound probe is inserted into the rectum with the aid of a stabilizing/stepper apparatus and transverse cross-sectional images of the prostate are acquired at fixed interval, i.e. 5 mm, increments from the base (low point) of the gland to the apex thereof.
For each cross-sectional image obtained, the boundaries of the prostate are manually outlined by a technician. The overall volume of the prostate is determined using well-known step section planimetric techniques. The boundaries of the prostate obtained during the volume study not only result in an accurate determination of the size and shape of the prostate, but also provide important information for developing the dosimetry radiation plan. The end result of the computerized dosimetry plan is an accurate map for placing the seeds within the gland.
The basic brachytherapy technique is well known, and is described in detail in several publications, including several U.S. patents, including: An article by Grimm, Blasko, Ragde, Slyvester and Clarke, titled Does Brachytherapy Have a Role in the Treatment of Prostate Cancer?, Hematology/Oncology Clinics of North America, Vol. 10, No. 3, June 1996, and U.S. Pat. No. 5,626,829 titled: Method and Apparatus For Interstitial Radiation of the Prostate Gland.
The contents of the above publications are hereby incorporated by reference. A second important step in preoperative evaluation for possible use of brachytherapy is the determination of pubic arch interference, referred to as PAI. The pubic bones meet centrally in the pelvis, and viewed from the perineum, they form an arch. The prostate is positioned behind this arch (again, as viewed from the perineum). In order for the seed implantation technique to be successful, the implant needles must be able to pass within the area between (interior of) the arch into the prostate gland. Significant pubic arch interference occurs when an arch is too narrow (or the prostate too large) to allow the passage of the implantation needles in many places. PAI may occur with both large and small prostate glands. However, typically in a normal sized male, PAI is rarely encountered when the prostate volume is less than 40 cc. When the prostate gland is above 60 cc, PAI is almost always encountered, and such patients first undergo either prostate shrinkage with hormones or select another form of treatment.
While the ultrasound probe can produce an accurate estimation of gland volume, it is unable to predict the position of the pubic arch. The current evaluation process requires that PAI be assessed using a separate CT examination, which is typically referred to as a "correlate" CT scan. In the CT scan, the position of the pubic arch in relation to the prostate is determined by outlining the prostate gland at its widest transverse cross-sectional dimension and superimposing this outline on the image of the pubic arch produced by the CT scan. Currently, clinicians use the rule of thumb of "more than one-fourth PIA" to determine whether a person can receive the seed implants, i.e. if the pubic arch covers more than one-fourth of the prostate gland, the technique is not used.
The correlate CT scan, however, while helpful to the clinician, is expensive and time-consuming. Not only is the scan itself expensive, but because patients are often initially prescheduled with a radiologist for a correlate CT scan, many of which are canceled following determination from the volume study that a particular prostate gland has a greater volume than 60 cc or smaller than 40 cc, a valuable time slot for the radiologist which could have been used for another patient is typically lost.
Further, because the position of the patient in the prostate brachytherapy procedure cannot be simulated in the CT scan machine due to inadequate space in the CT machine, the correlate CT scan can provide only a rough guideline of the actual configuration of the pubic arch. Hence, the determination of PAI using a CT scan is less accurate than is desirable and adds significantly to the overall expense of the brachytherapy treatment.
It is critical that PAI be accurately determined, as the brachytherapist will be forced to use a different template hole and to insert the needle at an angle to get past the pubic arch and to implant the seed as near to the target dosimetry position as possible if pubic arch interference is encountered during the brachytherapy procedure which was not determined by the initial pubic arch interference process. In prostate brachytherapy, there is only one opportunity to place the seeds correctly within the prostate, as the seeds which are implanted remain in the patient and cannot be removed. Hence, any obstruction problems caused by the pubic arch must be known prior to the seed implant procedure. While one or two needle insertions that deviate from the preplanned implant pattern will not typically affect the dose distribution, more than four obstructions/deviations are likely to affect the seed distribution and the optimal dose delivered to the prostate gland.
Hence, it is quite desirable that an accurate PAI assessment be made prior to beginning the seed implant procedure; it is also desirable to reduce the present cost of this part of the procedure.